This application claims the priority of Swiss application 964/99, filed in Switzerland on May. 25, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a vacuum treatment system having a vacuum treatment chamber, having elements for establishing a, treatment atmosphere in the chamber, and a sensor arrangement for detecting the treatment atmosphere momentarily existing in a treatment area in the chamber. The sensor arrangement ACTUAL value sensor of at least one of the elements is a regulating element of a control circuit for the treatment atmosphere, and having a workpiece carrier is moved in a driven manner through the, treatment area. The present invention also relates to processes for manufacturing workpieces in which the workpieces are moved in a treatment atmosphere guided by a control.
With respect to the vacuum treatment of workpieces, it is known to control the treatment atmosphere by one or several control systems concerning the maintaining of defined characteristics. This is particularly necessary if the processes taking place for the implementation of a desired treatment atmosphere in a vacuum treatment chamber are unstable per se in desired working points and can be stabilized only by way of a control. An example which is typical in this respect are reactive sputtering processes for coating substrates with non-conductive, thus typically oxidic layers, in the case of which a metallic DC-operated target, typically a magnetron arrangement is used in a reactive gas atmosphere. In addition to an inert working gas, such as argon, the reactive gas, such as oxygen or nitrogen, is fed to the treatment atmosphere. On the one hand, this leads to an intentional coating of the workpieces, for example, an oxide coating, but also to an interference coating of the metallic target. Without a working-point control, such a reactive sputtering process cannot be operated in a stable manner in the so-called transition mode or intramode. With respect to a detailed description of reactive sputtering processes in the above-mentioned transition mode, reference is made to U.S. Pat. No. 5,423,970, the disclosure of which is incorporated herein.
In such control systems, the control quantity (ACTUAL value measurement) is detected by measuring the plasma light emission, for example, in the case of a specific spectral line, by measuring the target voltage. A DESIRED value is defined for the measured control quantity and, corresponding to the control deviations, for example, the flow of reactive gas, in the above-indicated example, the oxygen flow (or, if it is not detected as a control quantity, the target voltage) is set as a regulating quantity in the control circuit. As a result, the operation, particularly a stabilization of the process in the desired working point, for example, in the above-mentioned transition mode, is achieved.
FIGS. 1 to 4 are schematic views of typical vacuum treatment systems of the latter type. They are systems of this type and workpiece manufacturing processes which can be implemented by vacuum treatment systems of this type and at which the problems to be described were recognized and solved according to the invention. The solutions according to the invention can, however, basically be used for systems and processes of the initially mentioned type in which the treatment process or the treatment atmosphere is controlled.
As illustrated by the arrow xcfx89, substrates 1 are moved in a workpiece carrier drum 3 rotating in a treatment chamber past at least one sputtering source 5. The sputtering source 5 with the metallic, thus electrically highly conductive target is, normally constructed as a magnetron source, DC-operated; often additionally with a chopper unit connected between a DC feeder generator and the sputtering source 5, as described in detail in EP-A-0 564 789, also incorporated by reference herein. A chopper unit intermittently switches a current path situated above the sputtering source connections to be of high resistance and low resistance.
In FIGS. 1 to 4, the DC generator and the optionally provided chopper unit are each illustrated in the blocks 7 of the sputtering source feed. In addition to a working gas GA, such as argon, a reactive gas GR, such as oxygen O2, is admitted to the treatment atmosphere U of the vacuum chamber, the reactive gas GR particularly by way of gas flow regulating valves 10.
Above the sputtering sources 5, a reactive plasma 9 is formed in which the substrates and workpieces 1 moved through by the drum 3 above the sputtering surfaces are sputter-coated. Because not only the substrates 1 are coated with the electrically poorly conductive reaction products formed in the reactive plasma 9 but also the metallic sputtering surfaces of the sputtering sources 5, the coating process described so far, particularly for achieving coating rates which are as high as possible, is unstable. For this reason, particularly in the case of these treatment processes and systems, the treatment process and, in this case, actually the treatment atmosphere acting upon the workpieces 1, is stabilized in the treatment area BB with a control.
As a possible implementation embodiment of such a control circuit according to FIG. 1, a plasma emissions monitor 12 measures the intensities of at least one of the spectral line or lines characteristics of the light emission from the reactive plasma 9. These intensities are fed as a measured control quantity Xa to a controller 14d.
In FIG. 2, the target voltage on the sputtering source 5 is measured as the measured ACTUAL quantity Xb of the control circuit by a voltage measuring device 16 and is fed to a controller 14b. With respect to the detection of the measured control quantity X, FIGS. 1, 3 and 2, 4 correspond to one another. At the controllers 14a and 14b, for forming control differences, the respective measured control quantities Xa and Xb are compared with the preferably adjustable guide values Wa and Wb, which correspond to the measured control quantities.
In accordance with the formed control differences at the controllers 14a and 14b and their amplification on transmission paths (not illustrated separately) dimensioned with respect to the frequency response according to the rules of control engineering, regulating signals are generated at the output side of the respective controllers 14a, 14b. As seen in FIGS. 1 and 2, the regulating signals, correspondingly marked Saa and Sba, are guided to the flow control valves 10 for the reactive gas as regulating elements which are set such that the respectively measured control quantities Xa and Xb are led to the values defined by the guide quantities Wa and Wb and are held there.
As seen in FIGS. 3 and 4, the regulating signal generated on the output side of the controllers 14a and 14b, which is correspondingly marked Sab and Sbb, is fed to the sputtering source feeds 7 which now themselves act as control regulating elements. This takes place either at their DC generators and/or at their optionally provided chopper units, where the chopper duty cycle is set.
The systems illustrated, for example, by FIGS. 1 to 4 are therefore vacuum treatment systems with a vacuum chamber, having elements for establishing a treatment atmosphere (specifically particularly a sputtering source and reactive gas feeds), and a sensor arrangement for detecting the treatment atmosphere momentarily existing in the chamber, the plasma emissions monitors and voltage measuring devices described as examples. The sensor arrangements ACTUAL-value sensors of at least one of the mentioned elements form a regulating element of one control circuit respectively for the treatment atmosphere.
For depositing electrically poorly conducting or non-conductive layers by way of the release of one layer material component of electrically conductive targets, an approach described in U.S. Pat. No. 5,225,057 involves first carrying out the metallic coating in spatially separated treatment stages and then oxidizing it in a reactive gas stage (an oxidation stage). In this known approach, there is no stability problem with respect to the coating process, but the system configuration consisting of several stages used for this purpose is relatively complicated.
As mentioned above, the present invention is based on treatment systems and manufacturing processes of the type explained by reference to FIGS. 1 to 4. It was demonstrated there that, particularly in the case of wide substrates of a width B larger than the dimension A in the same direction, preferably five times larger, and/or in the case of a small diameter of the substrate drum 3, along the substrate width B, because of the non-linear movement of the substrates in the area BB and relative to the sputtering source 5, a pronounced, approximately parabolic layer thickness distribution is obtained, as illustrated in FIG. 11a. This layer thickness distribution is known as a so-called xe2x80x9cchord effectxe2x80x9d.
The effective width of a substrate is its linearly measured dimension in the direction of its relative movement to the sputtering source 5. The corresponding effective sputtering source dimension A is its linearly measured dimension in the same direction. Furthermore, the above-mentioned substrate width B can definitely be taken up by several side-by-side smaller substrates. The addressed substrate 21 will then actually be a batch substrate.
In addition, it is stressed at this point that, for example, with a view to FIG. 1, the substrates may definitely be arranged on the interior side of a revolving carousel, which revolves around a sputtering source arrangement on a path which will then be concave with respect to the sputtering source arrangement. All foregoing statements and all following statements which are based on the drum arrangements according to FIGS. 1 to 4 analogously apply to the full extent to concave workpiece movements with respect to the sputtering source.
An object of the present invention is to implement, independently of the movement path and movement alignment of the workpieces moved in the treatment atmosphere, a desired layer thickness distribution in a targeted manner.
In a relevant vacuum treatment system, this object has been achieved in that at least one of the elements for establishing the treatment atmosphere, as a function of the workpiece carrier position, modulates the treatment atmosphere in the treatment area according to a given profile. Also, such a system or the related process, the control, for example, for stabilizing the treatment process, holds the treatment atmosphere in a DESIRED condition or working point. In contrast to U.S. Pat. No. 5,225,057, according to which, by the variation of the sputtering performance when depositing metallic layers, action is taken against the chord effect, in the present invention, a control resists a change of the treatment atmosphere.
In a first currently preferred embodiment of the vacuum treatment system according to the present invention, an adjustable DESIRED value defining unit is provided on the control circuit, as explained by reference to FIGS. 1 to 4, and the modulation provided according to the invention is implemented synchronously with the substrate movement by modulation of the DESIRED value.
In a further currently preferred embodiment of the systems according to the invention, the provided control is carried out more slowly than the treatment atmosphere modulation carried out according to the invention. Accordingly, the control of the xe2x80x9cdisturbance variablexe2x80x9d modulation cannot take place in a settling manner. The modulation introduced according to the invention, with respect to control engineering, is therefore the intentional introduction of a disturbance variable which is not to be settled.
If, as in the preferred system which is explained in FIGS. 1 to 4, the vacuum chamber comprises a sputtering source with an electrically conductive target and if a reactive-gas tank arrangement is connected to the chamber which reactive-gas tank arrangement has a reactive gas which reacts with the material released by the sputtering source to form a material with an electrically poorer conductivity as the coating material, the modulation preferably takes place at the electric source for the feeding of the sputtering source (its current or power), either, in the case of the preferred DC feeding, on the DC generator itself and/or at a chopper which is connected between the DC generator and the sputtering source and whose duty cycle is established.
In a further preferred embodiment, the system according to the invention, as a moved workpiece carrier, has a rotatingly driven carrier drum with workpiece receiving devices distributed on its periphery. The modulation is then synchronized with the drum revolving movement and is applied with a repetition frequency which corresponds to the workpiece carrier passing frequency.
Furthermore, a modulation form memory unit is preferably provided on the system according to the invention. This memory unit has at least one, preferably several previously stored modulation courses as well as a selection unit for the selective adding of the respectively desired modulation curves to the mentioned regulating element.
The process according to the invention of the initially mentioned type for manufacturing workpieces is characterized in that the treatment atmosphere in a treatment area of the workpiece moving path is modulated as a function of the workpiece position by a given profile.
The system according to the invention as well as the process according to the invention are particularly suitable for establishing a homogeneous layer thickness distribution on plane substrates of diameters B larger than the effective dimension A of the sputtering source or for producing defined layer thickness distributions on substrates, thus particularly also on substrates which are not plane. In addition, the present invention basically relates to processes for producing substrates, in which the chord effect is compensated on the substrates which are moved past the sputtering source on a circular path which is convex or concave with respect to a sputtering source.
The above-mentioned U.S. Pat. No. 5,225,057 also teaches modulating the sputtering performance of metallic targets for the compensation of the above-mentioned chord effect, specifically such that, in the case of substrates which are situated centrically with respect to the sputtering source, the sputtering performance passes through a maximum. More precise tests have indicated, however, that this type of modulation is not capable of compensating the addressed chord effect. Surprisingly, as will be demonstrated, the sputtering performance of the source must be modulated as a function of the substrate position such that, in the case of substrates situated centrally with respect to the sputtering source, the sputtering performance passes through a minimum.
Furthermore, manufacturing processes according to the invention are disclosed which particularly effects of the above-mentioned chord phenomenon, relative to a substrate movement which is convex or concave with respect to the sputtering source, are eliminated by a modulation of the reactive gas flowxe2x80x94in the preferably used reactive coating processesxe2x80x94and/or the working gas flow, i.e., the flow of an inert gas.
With respect to the modulation of the sputtering performance and a concave moving path of the substrates with respect to the sputtering source, when the workpieces are situated centrically with respect to the sputtering source, the sputtering performance is preferably modulated to a maximum.
Correspondingly, when the moving path of the substrates is convex with respect to the sputtering source, the reactive gas flow is modulated such that, with workpieces situated centrically with respect to the sputtering source, this flow passes through a maximum and if, in contrast, the substrate moving path is concave, it passes through a minimum.
If the working gas flow alone or in combination with the other defined modulation quantities is modulated according to the invention, this preferably takes place in such a manner that, in the case of a convex moving path of the substrates with respect to the sputtering source, while the workpieces are situated centrically with respect to the sputtering source, the working gas flow passes through a minimum, but, when the moving path is concave, it passes through a maximum.